Conventional electric plugs typically have two or three electrical contact prongs which are inserted into an electrical outlet receptacle or socket of conventional construction. The plugs are attached by a cord to the end application, such as an electrical appliance. Where such appliances are portable, it is desirable that the cord be of sufficient length to permit operation of the appliance at locations remote from the electrical socket.
For example, vacuum cleaners often have long cords so that vacuuming of large rooms or of rooms adjacent to where the electrical socket being used is located can be accomplished without continually unplugging and replugging the cord into closer electrical sockets. However, unless the cord is of such a length to permit the operator to complete the task while using only one socket, the operator must continually return to the particular socket in use to manually unplug the cord by grasping and pulling the plug from the socket, and replug the cord into a different socket that is closer to the next area to be worked on. This is a time-consuming and labor intensive process, especially in an industrial setting where it is repeated be each worker many times over the course of a work day.
In order to avoid the time and energy necessary to continually return to the socket in use and unplug the cord, many appliance operators pull on the cord itself at a location remote from the socket in an attempt to disengage the plug from the socket. However, such a procedure is obviously undesirable, as short circuits, bending of the electrical prongs, breaking of the wire, possible electric shock, etc. often result.
One attempt to solve the aforementioned problems is disclosed in U.S. Pat. No. 2,688,734. That patent teaches an electrically releasable electric connector in which a plunger is activated by a remote switch to project from the connector body between the two prongs of the plug and against the electrical socket. Of similar operation is the self-ejecting plug disclosed U.S. Pat. No. 3,475,715. However, each of these devices employs an ejecting mechanism that is located between the two electrical contact prongs. Consequently, the ejector must be made of a non-conducting material in order to avoid short circuiting. In addition, if the fit between the outlet receptacle and the electrical contact prongs is so tight that operation of the device results in only partial disengagement of the plug from the receptacle, there is a danger that the operator may receive an electrical shock in attempting to remove the plug from the receptacle, since the electrical prongs are exposed. When the plug falls to the ground upon ejection, the exposed prongs are liable to bend or break from the impact. Furthermore, each of the aforementioned prior art devices appears limited in application to two-pronged plugs; it is not at all apparent that the release mechanisms disclosed would function properly in plugs having three or more prongs.
An alternative construction is shown in U.S. Pat. No. 4,045,106, which discloses an automatic electric plug release in which the plug is spring loaded. By pulling on the cord, the terminal prongs are withdrawn into the mounting member. However, such a construction requires that the electrical contacts themselves be moveable. In addition, the user must pull on the cord at a position close to the socket, thereby requiring the aforementioned time-consuming and labor-intensive procedure of continually returning to the socket to disengage the plug.